Abstract Yoga, a physical activity based mind-body therapy has become increasingly popular as a preventive and therapeutic practice, making it one of the therapies with the most rapid increase in prevalence. Practice of yoga combines physical activity, modulated breathing and meditative exercises that combine to provide the practitioner a holistic mind-body experience. The effectiveness of yoga has been examined for a number of health outcomes, including stress, anxiety, depression, management of chronic conditions such as lower back pain and type 2 diabetes. Fewer studies have examined the effects of yoga practice on brain health and cognitive function. Age related cognitive decline is well documented. With the increasing population of older adults in the US, there is a need to not only test popular forms of exercise such as yoga, but also compare their efficacy with modalities such as aerobic exercise that have proven neurocognitive benefits. This research is timely in that yoga is a gentle and modifiable form of exercise that can be easily adapted for practice by older adults who may exhibit comorbidities or chronic health conditions that keep them from walking or performing other forms of aerobic exercise. To our knowledge, this is the first randomized control trial examining and comparing the effects of yoga and aerobic exercise training on behavioral and neurobiological correlates of cognitive function. We propose to conduct a 6-month randomized controlled exercise trial among older adults to compare the efficacy of yoga with aerobic exercise on cognitive function, brain structure and function, cardiorespiratory fitness, functional fitness, and inflammatory and molecular markers. Using a single-blind, three arm randomized control trail, 168 older adults ages 55-79 will be assigned to either: a Hatha yoga group, an aerobic exercise group or an active stretching and strengthening control group. The groups will engage in hour-long group exercise sessions 3x/week. A comprehensive neurocognitive test battery, brain imaging, cardiovascular fitness test, and a blood draw will take place at baseline; end of the 6-month intervention, and at 12-month follow-up. The proposed pilot RCT will examine the relationship between yoga training and improved cognitive functioning as well as identify neurobiological correlates as potential mechanisms of action through which yoga training exerts its effect on cognitive function. The investigative team is interdisciplinary, highly productive and has a history of collaboration in conducting exercise interventions examining neurocognitive outcomes in older adults.